The molds employed in the presses used for molding articles of plastic, rubber, elastomer, and other moldable materials are usually fabricated from mild steel. Stainless steel is not usually satisfactory, primarily because it does not have suitable heat transfer characteristics. The molds are usually cooled by chilled water flowing through passages formed in both halves of the mold assembly.
Any water condensation forming on the external surfaces of a mold of this kind is highly undesirable. The external surfaces of the mold halves are relatively cool, often only a few degrees above the temperature of the chilled water employed to cool the mold. Consequently, whenever the mold halves come into contact with moist ambient air, which is typical of the atmosphere in a molding plant, condensation is likely. This is particularly true in summer months or in warm climates. This condensation leads to rust formation on the externalFcavities will ruin the molded articles.
For most molding operations, therefore, it is highly desirable to maintain a dry atmosphere around the mold halves at all times. Moreover, this should be a warm atmosphere. Chilling the air around the mold is not desirable because this changes the thermal conditions for the molding process and tends to disrupt that process.
One rather obvious solution to this problem is to air condition the room in which the molding press is located. Expense, however, is usually an effective bar to this expedient. A number of proposals have been advanced to maintain a controlled atmosphere around the molds, using some sort of enclosure that is limited to the molding station of the press. If a fixed enclosure is employed, totally enclosing the entire molding station, however, the enclosure interferes with observation and servicing of the molds and other components of the molding station. On the other hand, if the enclosure is limited to the mold halves and their supporting platens, the expansion of the enclosure that occurs when the mold is opened to discharge molded products draws ambient air into the enclosure, so that the moisture condensation problem is not effectively eliminated. Furthermore, in most instances the enclosure requires extensive modification of the molding station of the press, which is undesirable from the standpoint of cost and may interfere with normal functioning of the press.
In most of the presses used in the plastic and elastomer molding industries, the opening of the two halves of the mold at the end of a molding cycle is followed by immediate discharge of the molded products from the molds. The molded products fall to the bottom of the molding station, into some form of product handling apparatus. This product handling apparatus may be a conveyor for transporting the molded products to an external sorting location. In other instances, the product handling apparatus may comprise an inlet hopper for a parts separator located adjacent to the press. In its simplest form, the product handling apparatus may comprise a receptacle for catching the molded products as they are discharged from the molds.
For any such product handling apparatus, there is often a tendency to lose some of the molded products. This is particularly true for multi-cavity molds employed in the manufacture of small molded parts such as container caps, syringe caps, and the like. Recovery of these parts is time consuming to a wasteful degree.
In many molding presses, the lubrication systems for the press components tend to leak or "weep", particularly from seals or bearing surfaces. If the lubricants contact the molded products, undesirable contamination results. The problem is particularly acute for molded products intended for food and drug use. For example, with molded products intended for use in medical appliances such as syringes, inadequate control of the products on discharge from the molds, resulting in contact with lubricants from the press or with other non-sterile materials, may create a need for subsequent cleaning and sterilization, increasing overall costs.